AN ALTERNATIVE METHOD OF STUDYING THE OPTICAL PROPERTIES OF HIGHLY NON-ABSORBING SPHERICAL MONODISPERSE AEROSOL USING A CELL TRANSMISSOMETER

An approximate and convenient experimental method of studying the basic optical properties of a highly non-absorbing monodisperse spherical aerosol has been developed using a cell transmissometer equipped with a laser beam at 632.8nm. The method is based on a linearization of the Lambert-Beer law which relates the light transmission measurements with the particle concentration measurements within the cell under stirred gravitational settling conditions. Applying Stokesʹ law, the diameter of the particles, which is needed as an input parameter, was deduced taking into account a parameterization procedure to evaluate the particle density. In order to have high scattering, spherical and monodisperse ammonium sulphate particles generated from a dilute solution and with a compressed-air nebulizer were used as test aerosol. A linear regression fit was applied to obtain values for the scattering and absorption coefficient efficiencies; as a result, the single-scattering albedo was evaluated and an indirect estimation of the refractive index, the asymmetry factor, the specific scattering coefficient, and the mass-scattering efficiency could be made. The method has the potential advantage of avoiding the use of instruments like integrating nephelometers as well as being applied to a highly non-scattering spherical monodisperse aerosol. Comparison with other methods indicates that the results are reasonably precise, and comparison with Mie calculations shows that the method is reasonably accurate.